Cancer is one of the world's largest health concerns. It is one of the major leading causes of deaths worldwide and together with cardiovascular diseases, diabetes, chronic respiratory diseases it causes over 60% of all deaths globally. Nearly 12.7 million new cancer cases and 7.6 million cancer deaths occurred in 2008 worldwide.
Colorectal cancer (CRC) is the third most common cancer in men and the second in women worldwide. Almost 60% of the cases occur in developed regions. Incidence rates vary worldwide, but are overall substantially higher in men than in women. Over 600 000 people die each year from the disease, accounting for 8% of all cancer-related deaths. In the US alone, over 150 000 new cases are diagnosed each year. Colon cancer is defined as cancer that forms in the tissues of the colon (the longest part of the large intestine). Most colon cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids).
Cancer of the colon is a highly treatable and often curable disease when localized to the bowel. Surgery is the primary form of treatment and results in cure in approximately 50% of the patients. Recurrence following surgery is a major problem and is often the ultimate cause of death. Nearly half of the colorectal cancer cases are metastatic or develop into a metastasized disease. In these cases, chemotherapy is the sole treatment option and the prognosis for the patient is often rather poor. Similarly, treatment regimens for other forms of cancer do not lead to full recovery of all patients and many cancers recur and/or develop into metastatic forms.
There is therefore a great need for new and improved drug-based therapies to combat not only colorectal cancer, but also a number of other cancer indications such as, for example, breast cancer, gastric cancer, gastrointestinal cancer, gall bladder cancer, bile duct cancer, colon cancer, rectal cancer, liver cancer, pancreatic cancer, head and neck cancer, esophageal cancer, mesothelioma cancer, lung cancer including non-small-cell lung cancer, ovarian cancer, endometrial cancer, cervical cancer, peripheral T-cell lymphoma (PTCL), melanoma, brain tumors, adenocarcinoma, esophageal cancer, and osteosarcoma.
The epidermal growth factor receptor (EGFR) is a tyrosine kinase that, when stimulated, activates several signaling pathways, including the MAPK, Akt and JNK pathways. Activation of the proteins involved in these pathways ultimately leads to DNA synthesis and cell proliferation, and the EGFR pathway has been shown to be activated in a wide variety of cancers, including CRC. Thus, EGFR is an attractive target for anti-cancer therapy. Several EGFR inhibitors have therefore been developed for use in cancer treatment. These include monoclonal antibodies such as cetuximab and panitumumab and the recently developed zalutumumab, nimotuzumab, and matuzumab, as well as small molecule drugs such as gefitinib, erlotinib, and lapatinib. Generally, the monoclonal antibodies bind to the extracellular ligand binding site of the EGFR, while the small molecules bind to and inhibit the intracellular tyrosine kinase part of the EGFR.
Cetuximab (Erbitux®) and panitumumab (Vectibix®) are monoclonal antibodies and EGFR inhibitors. They exert their inhibition by binding to the extracellular domain of EGFR, thus preventing binding of the natural ligand and activation of the receptor. Cetuximab is a chimeric mouse/human monoclonal antibody of the IgG1 isotype, while panitumumab is a fully human antibody of the IgG2 isotype.
Cetuximab is currently used for second and third line treatment of metastatic colorectal cancer (mCRC), in cases where the tumor expresses EGFR and wild-type KRAS (Kirsten ras sarcoma viral oncogene). KRAS is a guanosine triphosphate-(GTP-) binding protein downstream of the EGFR and is a central component of the mitogen-activated protein kinase (MAPK) pathway, which is a component of the EGFR signaling cascade. KRAS mutations lead to EGFR-independent constitutive activation of the signaling pathway and is associated with a lack of response and benefit from EGFR inhibitors such as cetuximab and panitumumab. Roughly 40% of colorectal cancers are characterized by a mutation in the KRAS gene. About 90% of these mutations occur in codons 12 and 13 in exon 2 of the KRAS gene, with the remaining mutations occurring in codons 61 and 146 (roughly 5% each).
Cetuximab has been shown useful to overcome acquired resistance to irinotecan chemotherapy and is thus used in combination with irinotecan in patients with mCRC that are refractory (resistant) to irinotecan. It is also used as a single agent in patients with mCRC after irinotecan and oxaliplatin-based regimens that have failed or in patients that are intolerant to irinotecan-based regimens.
Furthermore, cetuximab is used for treatment of patients with various stages of squamous cell carcinoma of the head and neck, either in combination with radiation therapy or together with or after platinum-based therapy.
Panitumumab is used for treatment of refractory EGFR-expressing metastatic colorectal cancer in patients with non-mutated KRAS, i.e. where other prior treatment has failed.
Although EGFR inhibitors initially held great promise as anti-cancer agents, and indeed still have valuable uses, they are also associated with some drawbacks. When used in a treatment naïve setting (i.e. in patients without prior treatment) as a single agent, the efficacy of cetuximab has been poor, not yielding any substantial improvement in survival of the patients. Also, when used in different combination treatments with e.g. FOLFIRI (5-fluorouracil (5-FU), leucovorin and irinotecan), FOLFOX (5-FU, leucovorin and oxaliplatin) or CAPOX (capecitabine and oxaliplatin), cetuximab improved survival times when combined with FOLFIRI, but yielded uncertain improvement in response rates or survival times for the other combinations (for review see Garrett and Eng, Expert Opin. Biol. Ther. (2011), vol. 11, pages 937-949).
The benefits of cetuximab treatment are more evident in a chemotherapy-refractory setting, i.e. where other treatments have failed, where cetuximab has been shown to improve response rates both when used as a single agent and in combination with irinotecan (Cunningham et al, N. Engl. J. Med. (2004), vol. 351, pages 337-345; Jonker et al, N. Engl. J. Med. (2007), vol. 357, pages 2040-2048). Improvement in survival in this setting was shown to be rather modest, i.e. a few months.
Cetuximab treatment is associated with some serious and some adverse side reactions, including severe allergic infusion reactions, cardiopulmonary arrest, dermatologic toxicity and hypomagnesemia (Garreth and Eng, Expert Opin. Biol. Ther. (2011), vol. 11, pages 937-949; Lenz, Biologics (2007), vol. 1, pages 77-91). The most frequently observed toxicity from cetuximab is rash; the majority of patients develop an acne-form rash, which can have a significant psychological impact on the patient. Other common side effects include pruritus, nail changes, headache, diarrhea, infections and vomiting. Similar side reactions are observed in relation to panitumumab treatment.
Thus, there is still a need to find new treatment regimens against cancer, as well as to improve the efficacy and reduce the side effects of EGFR inhibitors such as cetuximab and panitumumab.
Folates are endogenous substances that are essential for cell division and cell growth. Intracellular reduced folates exist as a pool of at least six interconvertable forms. Folates are for instance involved in nucleotide metabolism, where they serve as substrates and/or coenzymes of various enzymes, such as thymidylate synthase (TS) and dihydrofolate reductase (DHFR). The folate methylene-tetrahydrofolate (methylene-THF), for example, acts as a one-carbon donor in the conversion between dUMP and dUTP, performed by TS. Thereby it contributes to the synthesis of thymidine and thus to the synthesis of DNA and to cell growth.
The role of folates in carcinogenesis is complex. Experimental data suggest that the timing of folate supplementation during carcinogenesis is of importance (Ulrich, Cancer Epidemiol Biomarkers Prev (2006), vol. 15, pages 189-93; Kim, Gut (2006), vol. 55, pages 1387-1389). Although increases in folate levels before the existence of preneoplastic lesions (such as aberrant crypt foci or polyps in the colon) can prevent tumor development, folate supplementation is believed to enhance cancer progression once preneoplastic lesions are present. Thus, folates are believed to inhibit cancer development when used preventively, but believed to enhance cancer progression once cancer has started to develop. Since folates are known to be involved in synthesis of nucleotides and in cell growth, it has been expected that they have such cancer promoting effect. Furthermore, cancer cells frequently up-regulate folate receptors to meet their elevated need for nucleotides to support DNA synthesis and growth, hence an increased risk of tumor growth promotion with folate administration is expected (Ulrich, Am. J. Clin. Nutr. (2007), vol. 86, pages 271-273).
Antifolates, such as methotrexate and pemetrexed, have thus been used as chemotherapeutic agents for the treatment of cancer, by being able to inhibit one or more of the enzymes involved in the folate and nucleotide metabolism, e.g. TS and/or DHFR. Fluoropyrimidines, such as 5-fluorouracil (5-FU), has similarly been used as chemotherapeutic agents, by being able to inhibit TS. Antifolates as well as fluoropyrimidines are however cytotoxic and can be associated with severe side effects for many patients.
Folic acid and folates, such as in the form of leucovorin (also known as folinic acid), levoleucuvorin and methylene-THF, have been co-administered with chemotherapeutic agents to cancer patients. Folates have for example been used as rescue agents to methotrexate, in order to reduce the toxic side effects of the methotrexate and multi targeting anti-folate treatment (Borsi et al, Pediatric Hematology and Oncology 1990, vol. 7, pages 347-363; EP 1 699 462 B1).
Folic acid, leucovorin and methylene-THF have also been used in combination with 5-FU, in order to enhance the anti-tumoral effect of 5-FU.
U.S. Pat. No. 5,376,658, US 2007/0099866 A1 and WO 2007/064968 disclose the use of tetrahydrofolate (THF) and/or methylene-THF to enhance the cytotoxic and thus chemotherapeutic effect of 5-FU.
US2007/0280944 A1 discloses the use of methylene-THF in combination with 5-FU for the treatment of cancer, based on the finding that methylene-THF not only increases the efficacy of 5-FU, but also reduces the toxicity to the patient of 5-FU. In addition, at least one additional cancer drug is administered to the patient. The one additional cancer drug may for instance be an anti-EGFR antibody such as cetuximab.
WO 2008/109349 A1 discloses a treatment regimen for treating cancer, comprising administering 5-FU and methylene-THF to the patient certain days and administering capecitabine (marketed as Xeloda®) to the patient on the days in between. Capecitabine is analogous to 5-FU, but is administered to the patient orally. In certain embodiments the treatment further includes co-administration of a chemotherapeutic agent, e.g. cetuximab.
US 2011/0052581 A1 discloses a method for treating metastatic colorectal cancer by administration of picoplatin in conjunction with cetuximab and optionally with 5-FU and leucovorin.
Thus, cetuximab has been used in conjunction with 5-FU and folates, such as leucovorin and methylene-THF. In these treatment regimens the folates have been used in order to enhance the effect of 5-FU.